1. Field
Embodiments of the present invention relate to an electro-hydraulic brake system, and more specifically, to an integrated electro-hydraulic brake system that provides an actuator including a master cylinder, a pedal simulator, and the like, electronic stability control (ESC), and a hydraulic power unit (HPU) as a single unit.
2. Description of the Related Art
Recently, in order to improve fuel efficiency and reduce exhaust fumes, the development of hybrid vehicles, fuel cell vehicles, electric cars, and the like has been actively progressing. A brake device, that is, a brake device of an automotive brake system, is necessarily installed in such vehicles. Here, the automotive brake device refers to a device that reduces a speed of a running vehicle or stops the vehicle.
A brake device of a common automotive brake system includes a vacuum brake configured to generate braking power using a suction pressure of an engine and a hydraulic brake configured to generate braking power using a hydraulic pressure.
The vacuum brake is a device that may exert high braking power with a small force using a pressure difference between a suction pressure of a vehicle engine and an atmospheric pressure in a vacuum booster, and that is, a device that generates a much larger output compared to a force applied to the pedal when a driver presses a brake pedal. However, in the vacuum brake, the suction pressure of the vehicle engine needs to be supplied to the vacuum booster in order to generate a vacuum state. Therefore, fuel efficiency decreases and the engine needs to be constantly operated in order to generate a vacuum state even when the vehicle stops.
In addition, since the fuel cell vehicles and the electric cars have no engine, an application of an existing vacuum brake configured to amplify a pedal force of the driver while braking is unable. The hybrid vehicles need to introduce a hydraulic brake since an idling stop function needs to be implemented in order to improve fuel efficiency when the vehicle stops.
That is, as described above, all vehicles need to implement regenerative braking in order to improve fuel efficiency. When the hydraulic brake is introduced, implementation thereof is easy.
FIG. 1 illustrates an electro-hydraulic brake system which is a type of the hydraulic brake. In the electro-hydraulic brake system, when the driver presses the pedal, an electronic control unit detects the pressing, and a brake hydraulic pressure is delivered to a master cylinder and a wheel cylinder of each wheel, thereby generating braking power.
As illustrated in FIG. 1, the electro-hydraulic brake system includes units of an actuator 1 having a master cylinder 1a, a boosting unit 1b, a reservoir 1c, a pedal simulator 1d, and the like that control a brake hydraulic pressure delivered to a wheel cylinder 20, a modulator module 2 configured to independently control braking power of each wheel, and a hydraulic power unit (HPU) 3 having a motor, a pump, an accumulator, a valve, and the like. In this case, depending on a brake control method, an anti-lock brake system (ABS), a traction control system (TCS), an electronic stability control system (ESC), and the like may be selectively applied to the modulator module 2.
However, since each of the units 1, 2, and 3 constituting the electro-hydraulic brake system is separately provided and installed, an installing space needs to be secured due to a limited installing space of the vehicle, and a weight increases. Therefore, the electro-hydraulic brake system needs to secure the vehicle's safety, increased fuel efficiency, appropriate pedal feeling, and the like while braking, and an advanced electro-hydraulic brake system is required.
Meanwhile, when an out-valve configured to control a pressure of the wheel cylinder out of the valves used in the modulator module uses a normally close type-solenoid valve that normally maintains a close state according to a control characteristic, elasticity of a spring blocking a passage is large. In order to open the passage, since high current ranges need to be used, the control characteristic is deteriorated and heat generation is high.
Therefore, according to the above demands, research on development of an electro-hydraulic brake system that has a simple configuration, is able to smoothly implement braking power even when a failure occurs, and is easy to control is underway.